Connections to Chemistry Concepts (for correlation to course curriculum)
Medicinal chemistry—Medicinal chemistry focuses on the design and development of pharmaceuticals. A study of drug molecules and drug design could be coupled with a discussion of the increasing concern for the health effects of these compounds once they enter the water supply after excretion by the human body or after disposal.
History—Progress in the ability to measure smaller and smaller concentrations of contaminants in water and the development of disinfection and other water treatments can be traced through history. One can also research the cleanliness (or lack thereof) of drinking water throughout history, including its effects on the spread of sicknesses such as cholera.
Instrumentation—Methods of water testing and instrumentation used in testing could be discussed, including a comparison between tests that are qualitative, in that they only identify whether a substance is present or not, and those that are quantitative, in that they measure the amount of substance present. The sensitivity of testing can also be discussed. For example, a particular test may not be able to sense a very small concentration of a substance, even though that substance may be present.
Concentration—Measuring the amount of a particular substance in water involves the use of concentration units that may be unfamiliar to students. For example, many contaminants found in water may be of such minute amounts that it is more convenient to express the concentrations using parts-per-million, parts-per-billion, and beyond. These units can be compared to the most commonly-learned chemistry concentration unit, molarity.
Environmental chemistry—The topics of maintaining a clean and safe water supply through environmentally-conscious actions and continued advances in water testing and analysis are closely tied with environmental chemistry.
Possible Student Misconceptions (to aid teacher in addressing misconceptions)
“When you take a drug, your body uses all of the active ingredients.”When you take a drug, your body uses only a portion of the active ingredients. The rest is excreted. You release some of the drug into the sewer system when you flush the toilet.
“All drugs present in wastewater are from pills and liquid pharmaceuticals taken orally.”Medicated gels, creams, and lotions that we put on our skin are washed down the drain as we bathe. The antibacterial triclosan is also found in countless household products, including antibacterial soap, which can also enter the wastewater stream.
“The most widely-used prescription drugs are found in the highest concentrations in waterways.”Some of the most widely-used prescription drugs did not turn up in testing of waterways. Instead, drugs that are seldom used were among the top contaminants. The reason lies in the chemistry of wastewater treatment. Treatment plants normally disinfect wastewater with chlorine; chlorine completely removes some drugs, while others escape chlorine treatment.
“One method of treatment is able to remove all pharmaceuticals from water.”No single treatment is able to remove all pharmaceuticals from water, and some treatments have drawbacks. For example, chlorine only removes certain drugs and can react with pharmaceuticals to form more toxic compounds. Ozone removes 80% of all pharmaceuticals, but is expensive and has no residual effect. Pharmaceuticals in water can be minimized, but we will never remove every trace.
“Pure drinking water contains no additional substances.” Water that we consider “pure” enough to drink always contains additional substances. Limits are placed on how much of certain substances are allowed to be present in U.S. drinking water. However, these limits are rarely set at zero. Attaining this level of purity is cost-prohibitive, and in the case of certain substances, potentially unnecessary. Some bottled water manufacturers actually add certain minerals to their water to enhance its taste.
“The best way to dispose of unused medication is by flushing it down the toilet.”Flushed pharmaceuticals often reemerge in freshwater bodies. To minimize the environmental risk, guidelines now say that one should only flush or pour drugs down the drain if the accompanying patient instructions advise the user to. Other drugs should be removed from their containers, crushed, and mixed with an unappetizing substance, then sealed in a plastic bag, and thrown in the garbage.
Anticipating Student Questions (answers to questions students might ask in class)
“What can I do to help?”Being aware of the current concerns and guidelines regarding pharmaceuticals and personal care products is a good start. All of us can benefit from remembering that the pharmaceuticals and personal care products we purchase will potentially interact with our water supply, or will need to be properly disposed of if we don’t use all of the product. You could volunteer at a community take-back drug disposal event, or, if your community doesn’t offer one, investigate how such a program could be started.
“Where can I find information about my community’s water supply?”The EPA says that for community water systems, “Each year by July 1 you [your family] should receive in the mail a short report (consumer confidence report, or drinking water quality report) from your water supplier that tells where your water comes from and what’s in it” (http://water.epa.gov/lawsregs/rulesregs/sdwa/ccr/index.cfm). From that site, there are also links to see if your community’s report is posted on-line and frequent questions about the reports.
“Why do the disposal guidelines say to flush some drugs and not others?”Certain medicines may be especially harmful and, in some cases, fatal in a single dose if they are used by someone other than the person for which the medicine was prescribed. Flushing the medicines helps to immediately remove the drugs from the home.
“What happens to discarded pharmaceuticals after they are collected?” Typically, pharmaceuticals are taken to an approved facility for incineration.